#!/usr/bin/env bash

###############################################################################
#   Wrapper for Neovim that takes a lua (or vimscript) file as argument and   #
#     executes it. This essentially makes it possible to use Neovim as a      #
#   standalone interpreter and enables regular scripts to benefit from the    #
#    Neovim API (e.g. when used as a shebang). Without any arguments this     #
#                wrapper starts an interactive nvim lua REPL.                 #
###############################################################################

set -o errexit -o pipefail -o nounset
histfile=${XDG_DATA_HOME:-~/.local/share}/nvim/$(basename "$0")_history
compfile=${XDG_DATA_HOME:-~/.local/share}/nvim/$(basename "$0")_completion
COMP_WORDBREAKS="\"'><=;|&(){}+=*^/~ "

function send(){
  printf "%s\n" "$*" >& "${COPROC[1]}"
}

function hist(){
  case "$1" in
    load)
      mkdir -p "$(dirname "$histfile")"
      touch "$histfile"
      history -r "$histfile"
      ;;
    append)
      history -s -- "$2"
      history -a "$histfile"
  esac
}

function repl(){
  local cmd prefix
  while [[ -z "${cmd:-}" ]]; do
    read -Erp '> ' -d $'\r' || exit 0
    cmd=$REPLY prefix=""
    # hack to find out if the line can be interpreted as an expression to print
    # its value, similar to what lua 5.3 does (see
    # http://www.lua.org/manual/5.3/manual.html#7).
    if luajit -e "assert(function() return $cmd end)" 2>/dev/null; then
      prefix="="
    else
      # Extremely ugly hack to find out if statement should continue on next
      # line. Luajit error messages which expect statements to continue seem to
      # end with "'<eof>'".
      while [[ $(luajit -e "$cmd" 2>&1) == *"'<eof>'" ]]; do
        read -Erp '>> ' -d $'\r' || { cmd=''; break; }
        cmd+=$'\n'$REPLY
      done
    fi
  done
  hist append "$cmd"
  send verbose lua "${prefix:-}${cmd//$'\n'/ }"
  # Use SIGUSR1 to find out when vim finished processing cmd to continue the
  # repl
  send "!kill -USR1 $BASHPID"
}

# https://stackoverflow.com/a/52944692
function get_cursor_pos(){
    IFS='[;' read -p $'\e[6n' -d R -rs _ y x _
    printf '%s\n' "$x:$y"
}

function add_newline(){
  # vim doesn't insert newlines on eol, so we have to do it ourselves
  if [[ $(get_cursor_pos) != 1:* ]]; then
    printf '\n'
  fi
}

function complete_repl(){
  local word=
  if [[ -v COMP_WORDS ]]; then
    word=${COMP_WORDS[$COMP_CWORD]}
  fi

  send call "writefile([''] + getcompletion(${word@Q}, 'lua'), ${compfile@Q})"
  while [[ ! -s "$compfile" ]]; do :; done

  mapfile -ts 1 COMPREPLY <<< "$(< "$compfile")"
  if [[ $word == *[.:]* ]]; then
    local stem=${word%[.:]*}
    for i in "${!COMPREPLY[@]}"; do
      COMPREPLY[i]="${word::((${#stem}+1))}${COMPREPLY[i]}"
    done
  fi

  rm "$compfile"
}

case "${1:-}" in
  "") # without arguments start interactive repl
    hist load
    nvim --version | sed '/^$/,$d'
    coproc nvim -es -i NONE
    trap "add_newline && repl" SIGUSR1
    complete -o nospace -IF complete_repl -EF complete_repl -DF complete_repl
    repl
    # use a loop as wait returns when a signal with a trap is received
    until wait; do
      :
    done
    ;;
  --help|-h)
    printf "%s\n%s\n  %s\n" \
      "usage: $(basename "$0") [options] [script [args]]" \
      "Available options are:" \
      "-h  print this help message and exit (also --help)"
    ;;
  *) # treat arg as a file
    # use 'echo""' to append a final end-of-line indicator
    exec nvim -c 'autocmd VimLeave * :echo ""' -l "$@"
esac